Expansion Joints
A permanent solution shouldn't be required for a temporary problem.
A permanent solution shouldn't be required for a temporary problem.
Concrete structures need to move. Concrete shrinkage, post-tensioning and temperature changes create movement that must be accommodated during construction. Traditionally, an expansion joint provides that freedom by permanently separating portions of the structure.
The Problem
The movement is greatest during the early life of the structure, but the conventional solution leaves a permanent joint in the building. That means sealants, covers, potential leakage and ongoing maintenance for the life of the structure.
A Better Solution
PS=Ø-EJ allows the structure to move during construction. After the building is enclosed and the appropriate initial movement has occurred, the reinforcement is connected to restore structural continuity, eliminating the permanent expansion joint where appropriate.
Eliminating the permanent open joint where appropriate also eliminates the associated sealant line, reducing the potential for leakage and ongoing joint maintenance.
Build Better.
How Expansion Joints Are Filled, Caulked, and Sealed
Filling an expansion joint in concrete means placing a compressible material in the gap and sealing the top so water stays out while the joint still opens and closes. If your slab has a permanent expansion joint, filling and caulking it correctly is the right thing to do, and on many structures a permanent joint is genuinely required. Here is how the standard detail works, and where a different approach removes the maintenance entirely.
What filling, caulking, and sealing an expansion joint involves
A joint that is meant to stay permanent is filled with a compressible material so the slab can expand and recover without crushing at the interface, then the top of the joint is sealed against water. The sequence most crews follow looks like this:
- Clean the joint face. Old sealant, debris, and loose material come out first. A sealant will only bond to a clean, sound joint face, which is why a reseal almost always starts with removal.
- Set the compressible filler. A backer material fills the gap so the slab can still move, while controlling how deep the sealant sits on top.
- Caulk and seal the top. A flexible sealant caps the joint so water cannot reach the gap, while still stretching and compressing as the joint cycles with temperature.
- Re-set covers and nosings on trafficked joints. Cover boards and nosings wear under traffic and get re-set as part of the same cycle.
Why the sealant, not the concrete, is what fails
When a filled expansion joint starts to leak, the concrete is rarely the culprit. The failure starts at the sealant. Joint sealant is a consumable: it hardens, shrinks, and pulls away from the joint face over time. It was never meant to last the life of the slab, which is why it lands on the maintenance schedule. The joint opens and closes with every thermal cycle, and each cycle works the sealant loose a little more until the bond breaks and the gap is open to water. Freeze-thaw cycling then widens the crack, and on a structural deck that water eventually reaches the reinforcement, which is where a cosmetic problem turns into a durability problem.
Filling and caulking a joint is maintenance of a permanent condition. The question we ask at design is whether that permanent condition has to exist at all.
The alternative: remove the joint instead of maintaining it
Filling and resealing manage a joint that stays in the building. PS=Ø-EJ takes a different path on reinforced and post-tensioned work. It lets the structure move during construction, when movement is greatest, then connects the reinforcement once the appropriate initial movement has occurred, restoring structural continuity and eliminating the permanent joint where appropriate. Eliminating the permanent open joint where appropriate also eliminates the associated sealant line, reducing the potential for leakage and ongoing joint maintenance for the life of the structure. No permanent joint means no filler to compress, no caulk to reseal, and no sealant line to inspect and replace on a cycle.
To be clear about scope: PS=Ø-EJ is a design-stage decision for new reinforced and post-tensioned structures, not a repair product for an existing filled joint. Where a permanent joint is genuinely required, filling and caulking it correctly is the right call. Where it is not, a self-supporting splice removes it. Not sure which bucket your project is in? Call (800) 355-8414 and our engineers will tell you straight.
Expansion Joint vs. Control Joint vs. Movement Joint
These terms get used interchangeably on jobsites, but they are not the same. Movement joint is the category. Expansion and control joints are two different members of it. Here is how they line up.
| Joint | What It Is | Movement It Handles |
|---|---|---|
| Expansion joint | A full-depth gap between sections, filled and sealed | Thermal growth as the slab heats |
| Control (contraction) joint | A tooled or saw-cut weakness in the surface | Drying shrinkage, steering where cracks form |
| Construction joint | Where one pour stops and the next begins | Stops between placements poured on different days |
| Movement joint | The umbrella term for all of the above | Any planned concrete volume change |
Every expansion joint and every control joint is a movement joint, but they solve different problems. For the full breakdown of all four types and spacing, see concrete movement joints.
Expansion Joint FAQs
What is an expansion joint in a concrete slab? +
An expansion joint in a concrete slab is a deliberate full-depth gap left between two pours so the adjoining sections can move independently as the concrete shrinks during curing and grows or contracts with temperature. The gap is filled with a compressible material or sealant so that movement does not crack the surrounding slab. On reinforced and post-tensioned structures, PS=Ø-EJ replaces that permanent gap with a mechanical rebar splice: the structure still moves during construction, then the reinforcement is connected once the appropriate initial movement has occurred, eliminating the permanent joint where appropriate.
How often do expansion joints need resealing? +
A conventional expansion joint has a sealant line that has to be inspected, cleaned, and replaced on a cycle for the life of the structure. Joint sealant is a consumable. It hardens, shrinks, and pulls away from the joint face over time, and it was never meant to last the life of the slab, which is why it lands on the maintenance schedule. Cover boards and nosings on trafficked joints wear and get re-set as well. The exact interval depends on exposure, traffic, and the sealant specified, so the building team sets the schedule. Eliminating the permanent open joint where appropriate removes that resealing line item entirely.
What is the difference between an expansion joint, a control joint, and a movement joint? +
Movement joint is the umbrella term for any joint that accommodates concrete volume change. A control joint, also called a contraction joint, is a tooled or saw-cut weakness that tells a slab where to crack so drying-shrinkage cracks form where you want them. An expansion joint is a full-depth gap that lets adjoining sections move independently, mainly to handle thermal growth. A construction joint is simply where one pour stops and the next begins. So every expansion joint and every control joint is a movement joint, but they solve different pieces of the same problem. PS=Ø-EJ targets the case where reinforcement has to be carried across that interruption, restoring the structural connection where appropriate once the initial movement has occurred.
Can you fill or caulk an existing expansion joint, or does it have to be eliminated? +
Filling and caulking are the standard way to maintain a joint that is meant to stay permanent, and on many structures a permanent joint is genuinely required. PS=Ø-EJ is not a repair product for an existing filled joint. It is a design-stage decision for new reinforced and post-tensioned work, where the structure is allowed to move during construction and the reinforcement is then connected to restore continuity, so the permanent joint, and the sealant line that comes with it, never has to exist in the first place. Our engineers can walk a project team through where a joint is genuinely required versus where a splice removes it.